1. Field of the Invention
The present invention relates to accelerometers. More particularly, the present invention relates to a multi-axis accelerometer comprising a mass suspended by springs above an optical sensor.
2. Description of the Prior Art
Conventional accelerometers may be too limiting for certain applications. Conventional piezoelectric accelerometers, for example, can only detect a linear acceleration in one axis. Multiple piezoelectric accelerometers can be used to detect linear accelerations in multiple directions, as well as learn a correlation between the sensors"" signature and a rotational acceleration. However, learning the correlation requires a time consuming calibration or adaptation procedure and the resulting estimate is typically not reliable. Conventional capacitive accelerometers having a xe2x80x9cspoke and wheelxe2x80x9d configuration are typically very sensitive to noise, very expensive to manufacture, and can detect only rotational accelerations and not linear accelerations.
There is, therefore, the need for an improved accelerometer capable of accurately detecting linear as well as rotational accelerations.
The present invention may be regarded as a multi-axis accelerometer comprising at least one optical sensor for generating a sensor signal in response to light illuminating the optical sensor, a mask positioned over the optical sensor for covering a first area of the optical sensor, at least one spring, and a mass suspended above the optical sensor by the spring. The mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask. When the multi-axis accelerometer accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.
In one embodiment the optical sensor and mask are integrally formed. In one embodiment, the at least one mass aperture comprises a plurality of linear apertures, and the mask comprises a corresponding plurality of opaque lines.
In one embodiment, the at least one spring comprises a vertical wire having a first end connected to the mass and a second end connected to the optical sensor.
In one embodiment the at least one optical sensor comprises an A sensor, a B sensor, a C sensor and a D sensor. The A sensor generates an A sensor signal, the B sensor generates a B sensor signal, the C sensor generates a C sensor signal, and the D sensor generates a D sensor signal. A first linear acceleration is detected relative to the A sensor signal and the D sensor signal, a second linear acceleration is detected relative to the B sensor signal and the C sensor signal, and a rotational acceleration is detected relative to the A, B, C and D sensor signals. In one embodiment, the first linear acceleration is detected relative to a difference between the A sensor signal and the D sensor signal, the second linear acceleration is detected relative to a difference between the B sensor signal and the C sensor signal, and the rotational acceleration is detected relative to a first sum generated by summing the A sensor signal and the D sensor signal, a second sum generated by summing the B sensor signal and the C sensor signal, and a difference between the first sum and the second sum.
In another embodiment, the multi-axis accelerometer further comprises a housing for creating a compartment between the optical sensor and the mass, and a fluid fills the compartment for providing a damping effect. In one embodiment, the at least one spring comprises a horizontal wire having a first end connected to the mass and a second end connected to the housing.
The present invention may also be regarded as a method of detecting linear and rotational accelerations. The method comprises the steps of positioning a mask over an optical sensor to cover a first area of the optical sensor, suspending a mass above the optical sensor using springs, and illuminating the optical sensor with light to generate a sensor signal. The mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask. When the multi-axis accelerometer accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.
The present invention may also be regarded as a disk drive comprising a disk, a head, an actuator for actuating the head radially over the disk, and a multi-axis accelerometer for generating an acceleration signal representing a vibration affecting the actuator. The acceleration signal for controlling operation of the disk drive. The multi-axis accelerometer comprising at least one optical sensor for generating a sensor signal in response to light illuminating the optical sensor, at least one spring, and a mass suspended above the optical sensor by the spring. The mass comprises at least one mass aperture for allowing the light to pass through the mass aperture and illuminate a second area of the optical sensor not covered by the mask. When the disk drive accelerates causing the mass to move, a corresponding movement of the mass aperture alters the illumination of the optical sensor such that the sensor signal is indicative of the acceleration.